Characterization and Mechanisms of H2S and SO2 Adsorption by Activated Carbon

Coconut-shell-based activated carbon (ACS-1) was used as a sorbent to simultaneously remove H2S and SO2 from simulated Claus tail gas. Adsorption and regeneration tests were performed to systematically investigate the desulfurization performance, regenerability, and stability of the ACS-1 sorbent. The physicochemical properties of ACS-1 before and after adsorption were characterized by nitrogen adsorption, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The experimental results revealed that the ACS-1 sorbent exhibited good desulfurization performance under a feed gas of H2S (20 000 ppmv), SO2 (10 000 ppmv), and N-2 (balance), and the concentrations of H2S and SO2 in the simulated Claus tail gas could be reduced to less than 10 mg/m(3) by ACS-1. The breakthrough sulfur capacity of ACS-1 is 64.27 mg of S/g of sorbent at an adsorption temperature of 30 degrees C and a gas hourly space velocity of 237.7 h(-1). The micropores with sizes of around 0.5 nm in ACS-1 are the main active centers for adsorption of H2S and SO2, whereas mesopores have little desulfurization activity for deep removal of H2S and SO2. Both physical adsorption and chemical adsorption coexisted in the process of desulfurization. The majority of sulfides were removed by physical adsorption, and 11% of the sulfur compounds existing in the form of elemental sulfur (ca. 20 atom %) and sulfate (ca. 80 atom %) were derived from the chemical adsorption. The mechanism of H2S and SO2 adsorption on the ACS-1 sorbent is also discussed. H2S and SO2 are first adsorbed on ACS-1 by physical adsorption and then partially oxidized to elemental sulfur and sulfate, respectively, by the oxygen adsorbed on ACS-1. At the same time, the Claus reaction between H2S and SO2 occurs. In addition, the ACS-1 sorbent can be completely regenerated using water vapor at 450 degrees C with a stable breakthrough sulfur capacity during five adsorption-regeneration cycles.